Safety switch assembly

ABSTRACT

The safety switch unit controls the source of power for machinery in accordance with the opening and closing of a room door. The safety switch includes an actuator (2) secured to a door, a cam shaft extending transversely of a direction in which the actuator (2) advances into the switch unit (1), the actuator (2) having a stepped top end in correspondence to which cam plates (13), (14a) and (14b) are provided within the switch unit (1) each capable of independently rotating, these cam plates having start sides (17) and (22) and a single cam follower pin (29) passed therethrough, thus protecting the switch unit (1) against mischievous or malicious operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a safety switch for use in stoppingmachinery in any emergency so as to protect the operators against anaccident which may result in injury or death.

2. Background Art

In factories or any sites where machinery is in operation, various typesof safety switch are used so as to stop the machinery when any emergencyoccurs, or when a normally shut room door is carelessly left open orwhen a protective cover of the machinery is carelessly left open.

For example, PCT 90/08396 Publication (laid open on Jul. 26, 1990)discloses a safety switch using a pair of locking cams that are expandedsideways in response to the entry of an actuator. Japanese patentPublication (allowed) No. 1-24332 (published on May 11, 1989) disclosesa safety switch also uses locking cams that are expanded in response toentry of an actuator. A disadvantage in common with these two prior artsafety switches is that the body must be large enough to allow for theexpansion of the arms.

The known switches are designed to shift a movable contact point from afixed contact point to the other fixed contact point in accordance withthe entry of an actuator but the problem is that deenergization islikely to occur before the door is completely locked.

THE SUMMARY OF THE INVENTION

According to the present invention, the safety switch assembly controlsa source of power for machinery in accordance with the opening (orclosing of) a room door, a cover or any other means provided forprotecting workers against danger. The switch assembly, compact in size,switches off the machinery when the protective door is opened or when itis left half open, wherein the movement or the position of the door istransmitted to the switch assembly through an actuator secured to thedoor, the actuator being shaped to a unique form which can not be sharedby any other thing, thus protecting the switch assembly againstmischievous or malicious operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a switch assembly embodying thepresent invention;

FIG. 2 is a plan view showing the operating block and the contact-pointblock of the switch assembly with the cover being removed;

FIG. 3 is a cross-sectional view taken along the line 3--3 in FIG. 2;

FIG. 4 is a cross-sectional view taken along the line 4--4 in FIG. 2;

FIG. 5 is a plan view of the contact-point block showing the internalstructure thereof;

FIGS. 6(a) to 6(e) are diagrammatic views showing the interaction of theactuator and the cam plates in the switch assembly;

FIGS. 7(a) to 7(d) are diagrammatic views showing the interaction of thecam plates and a substitute actuator;

FIGS. 8(a) to 8(d) are diagrammatic views showing the interaction of thecam plates and another substitute actuator;

FIGS. 9(a) and 9(b) are diagrammatic views showing a modified version ofthe operating section of the switch assembly;

FIG. 10 is a plan view exemplifying the locking mechanism using a locklever;

FIG. 11 is a vertical cross-sectional view taken along the line 11--11in FIG. 10;

FIGS. 12(a) to 12(c) are diagrammatic views showing the interaction ofthe actuator and the cam plates;

FIG. 13 is a cross-sectional view showing a delay mechanism in theswitch section in the contact-point block;

FIG. 14 is a perspective view showing a portion of the delay mechanismshown in FIG. 13;

FIGS. 15(a) to 15(d) are diagrammatic cross-sectional views showing theprocess of interaction of the delay mechanism shown in FIG. 13, when thedoor is closed;

FIGS. 15(a)' to 15(d)' are diagrammatic plan views respectivelycorresponding to FIGS. 15(a) to 15(d);

FIGS. 16(a) to 16(d) are diagrammatic cross-sectional views showing theprocess of interaction of the delay mechanism shown in FIG. 13, when thedoor is opened;

FIGS. 16(a)' to 16(d)' are diagrammatic plan views respectivelycorresponding to FIGS. 16(a) to 16(d);

FIG. 17 is a plan view showing another modified version of a switchsection in the contact-point block;

FIG. 18 is a cross-sectional view taken along line 18--18 in FIG. 17;and

FIG. 19 is a cross-sectional view taken along the line 19--19 in FIG.17.

BEST MODE OF EMBODIMENT

Referring to FIG. 1, a switch assembly 1 is attached to a wall at aplace near to a protective door (not shown) in such a manner as toenable an actuator 2 secured to the door. When the door is closed, theactuator is inserted in the switch assembly 1 and locked therein,thereby locking the door. The door is unlocked only when the actuator 2is disengaged from the switch assembly 1. The switch assembly 1 has twoslits 6a and 6b which allow the entry of the actuator 2. The slits 6aand 6b are produced in planes crossing at right angle. Either slit 6a or6b is selected depending upon the position of the door. The switchassembly 1 includes an operating block 4, a contact-point block 3, andan actuator releasing block 10, which are mutually detachably coupledtogether by means of screws in the form of a box as seen from FIG. 1.The contact-point block 3 is provided with a lens 83 as a lightingindicator. The actuator 2 includes a base plate 5 joined to the door(not shown). The base plate 5 includes operating portions 7a and 7bwhich are inserted into the switch assembly 1. The portion 7a is arecessed portion, and the portion 7b are projecting portions, with therecessed portion 7a interposed therebetween. The base plate 5 isprovided with an aperture 8 designed to accept lower parts of the camplates 13, 14a and 14b so as to release them from a locking mechanism,which will be referred to below. The aperture 8 has a wall portion 9toward the switch assembly 1, which functions to enable the actuator 2to return to its original position after it is disengaged from theswitch assembly 1.

Referring to FIGS. 2, 3, and 4, the operating block 4 includes a pair ofsupports 11 which supports a cam shaft 12 carrying a first cam plate 13,and a pair of second cam plates 14a and 14b, all of these cam platesbeing independently rotatable. The independent rotation is effected bywashers inserted between the first cam plate 13 and the second camplates 14a, 14b. Each of the second cam plates 14a and 14b has a springagainst the support 11. The springs bias the second cam plates 14a and14b to return to its original position.

As more clearly shown in FIGS. 4 and 6, the first cam plate 13 has tworecesses of the same shape which receive the actuator 2; onecorresponding to the slits 6a and the other corresponding to the slit6b, each recess having sides 17 and 18 wherein the sides 17 work to putthe cam plate 13 into operation and the sides 18 work to return the camplate 13 to its original position. Hereinafter, the sides 17 will bereferred to as "start sides" and the sides 18 as "return sides". The camplate 13 has a sectorial recess 19 about at 90° so as to enable anoperating rod 27 to play therein. The sectorial recess 19 has a camgroove 20 in the bottom wall. The cam groove 20 receives a cam followerpin 29 secured to the operating rod 27, the follower pin 29 beingslidable in the groove 20. The cam groove 20 has a pin rest hole 21 atthe starting end; in FIG. 6(a) it will be seen that the pin rest hole 21is slightly bulged to the right. The second cam plates 14a and 14b havestart sides 22 and return sides 23, and cam grooves 24 which has a pinrest hole 25 bulged to the right in FIG. 7. The cam follower pin 29passes through the cam grooves 20 and 24.

As shown in FIG. 3, there is provided an L-shaped post 26 fixed behindthe cam plates 13, 14a and 14b, the guide 26 including a pair of posts26a erected on each side. Each post 26 has a guide slot 26b in which thefollower pin 29 is shiftable. The operating rod 27 referred to above isdisposed along the guide 26, with a spring 27a at the center which isadapted to receive a spring. The operating rod 27 is retractablyinserted into a casing 34 which houses a switch section 33. Theoperating rod 27 is integral with the cam follower pin 29 projectingcrosswise thereof and the cam follower pin 29 passes through the camgrooves 20 and 24 of the cam plates 13, 14a, and 14b and are supportedby the guides 26 on both sides. Thus the operating rod 27 is preventedby the guides 26 from swinging sideways while it moves forward andbackward (right and left in FIGS. 3 and 4). The operating rod 27 isprovided with a hook 27b at the rear end, which is engaged with a hook46 of a switching rod 39. The operating rod 27 and switching rod 39 isnormally connected by engagement of the hooks 27b and 46 so as to effecta unitary movement. The space existing between the spring 27a and aswitch case 28 is sealed against water by a rubber bellows 30. Outsidethe bellows 30, a spring 32 is disposed between the spring 27a and abase 31 of the bellows 30, so as to bias the operating rod 27 forward(to the left in the drawings). When the operating rod 27 is fullyshifted to the left as shown in FIGS. 3 and 4, the follower pin 29 fitin the pin rest holes 21 and 25 of the grooves 20 and 24. Hereinafter,this stage will be referred to as the "initial stage". At this initialstage, the cam plates 13, 14a and 14b are ready to receive the operatingportions 7a and 7b of the actuator 2 with the follower pins 29 ready toslide in and along the cam grooves 20 and 24.

Now, referring to FIGS. 4 and 5, the contact-point block 3 will bedescribed:

The contact-point block 3 includes the switch case 28 referred to abovewhich houses a switch section 33. The switch section 33 includes a pairof terminal plates 36 having fixed contact points 35 with which movablecontact points 41 are normally kept in contact. A pair of terminalplates 38 having fixed contact points 37 with which movable contactpoints 43 are brought into contact when the switching rod 39 is workedin a manner described below. The switching rod 39 is provided withterminal plates 42 and 44 having the contact points 41 and 43, theterminal plates 42 and 44 being passed through an aperture 40 and spacedby a spring 45. The switching rod 39 is slidable axially with the switchassembly 1. As described above, the operating rod 27 and switching rod39 can move as an assembly by engagement of the hooks 46 and 27bthereof. The contact points 35 and 41 are normally kept in contact witheach other, and the contact points 37 and 38 are normally separated asshown in FIG. 5. The terminal plates 36 and 38 are electricallyconnected to a source of power for a machine (not shown) to becontrolled by the switch assembly 1.

Referring to FIGS. 6 to 8, an example of the operation of the switchassembly 1 will be described:

While a protective cover (not shown) is opened, intentionally orcarelessly, the actuator 2 becomes withdrawn from the switch assembly 1.This state is shown in FIGS. 2 to 4. The operating rod 27 and switchingrod 39 are shifted forward (to the left) as shown in FIGS. 2 to 4 underthe action of the spring 32, thereby enabling the cam follower pin 29 torest in the pin rest holes 20 and 24 of the cam grooves 20 and 24. FIG.6(a) shows this initial stage where the sides 17 of the cam plates 13and the side 22 of the cam plates 14a and 14b are not in the same levelbut they receive the recessed portion 17a in the side 17 and theprojecting portions 17b in the side 20. FIG. 5 shows the switch section33 at this stage where the contact points 35 and 41 are kept in contactunder the action of the spring 45, and the contact points 43 stand awayfrom the fixed contact points 37.

When the protective door is closed, the actuator 2 advances into theswitch assembly 1 by a distance D (FIG. 6(a)) through the slit 6a (or6b), the portions 17a and 17b of the actuator 2 come into engagementwith the sides 17 and 22 of the cam plates 13, 14a, and 14b. In FIGS.6(a) to 6(e) the arrow C indicates the direction in which the camfollower pin 29 slide in and along the guide slots 26b of the post 26 inaccordance with the movement of the cam follower pin 29 in and along thegrooves 20 and 24. D2, D3, D4 and D5 denote the distances between thecam shaft 12 and the cam follower pin 29.

The actuator 2 is further advanced into the switch assembly 1, therebyenabling the cam plates 13, 14a and 14b to rotate. The follower pin 29is shifted in and along the cam grooves 20 and 24, and moves in thedirection C in and along the guide slots 26b. The distance D1 changesinto a distance D2 as shown in FIGS. 6(a) and 6(b). The operating rod 27and switching rod 39 are moved together backward (to the right), therebyseparating the movable contact points 41 from the fixed contact points35. The operating rod 27 can smoothly move because of the lessfrictional two-point support by the posts 26 and switch case 28.

When the cam follower pin 29 stands away from the cam shaft 12 by adistance D3 (FIG. 6(c)) where the pin 29 reaches a middle point of thegrooves 20 and 24, the contact points 35 and 41 are separated from eachother in accordance with the backward movement of the switching rod 39.When the distance becomes D4 (FIG. 6(d)), the contact points 43 comeinto engagement with the contact points 37 under the action of thespring 45. When the actuator 2 is completely inserted into the switchassembly 1, the distance between the cam shaft 12 and the pin 29 reachesD5 (FIG. 6(e)), which is the maximum.

When the contact points 43 are brought into engagement with the contactpoints 37, parts of the cam plates 13, 14a and 14b fit in the aperture 8of the actuator 2 where the return sides 18 and 23 are opposed to thewall portion 9 of the aperture 8. When the door is opened thereby tocause the actuator 2 to withdraw from the switch assembly 1, the wallportion 9 pushes the return sides 18 and 23 to cause the cam plates 13,14a, and 14b to rotate in the clockwise direction in FIG. 6. Therotation of the cam plates 13, 14a and 14b are accompanied by theforward movement of the operating rod 27 and switching rod 39, therebyseparating the contact points 43 from the contact points 37. In this wayit is ensured that the contact points 37 and 43 are opened in accordancewith the withdrawal of the actuator 2 from the switch assembly 1.

FIGS. 7 and 8 show a case where the actuator 2 is replaced by anordinary screw-driver 48 for insertion into the switch assembly 1. FIG.7(a) to 7(d) show the process of operating the cam plate 13 alone (thecam plates 14a and 14b are left stationary) wherein like referencenumerals designate like components to those throughout FIGS. 1 to 6. Theother side of the cam plate 13 is also omitted from illustration.

The driver 48 is inserted by hand into the switch assembly 1 through theslit 6a (FIG. 7(a)) and comes into abutment with the start side 17 ofthe cam plate 13. The further insertion of the driver 48 causes the camplate 13 to rotate so that the cam follower pin 29 is shifted in andalong the guide slot 26b of the posts 26 in the direction C (FIGS. 7(b)and 7(c)). The pin 29 fits in the pin rest holes 25 of the cam plates14a an 14b which remain stationary (FIG. 7(d)) whereby the movement ofthe pin 29 in the direction C is stopped. Thus the cam plates 13, 14aand 14b are stopped from rotation. The same takes place when any othertool than a screw driver is used.

FIG. 8 shows a case where the cam plate 14b alone is tried to rotate bya screw-driver 48 with the cam plates 13 and 14a remaining stationary.The screw driver 48 is inserted by hand into the switch assembly 1through the slit 6a (FIG. 8(a)) and comes into abutment with the startside 22 of the cam plate 14b. The further insertion of the driver 48causes the cam plate 14b to rotate so that the cam follower pin 29 isshifted in and along the guide slot 26b of the post 26 in the directionC (FIGS. 8(b) and 8(c)). The pin 29 fits in the pin rest holes 21 of thecam plate 13 which remain stationary (FIG. 8(d)) whereby the movement ofthe pin 29 in the direction C is stopped. The non-rotation of the camplates 13 and 14a is maintained, and the cam plate lab is stopped fromrotation.

Referring to FIGS. 9(a) and 9(b), another example of the embodiment willbe described wherein like reference numerals designate like componentsto those throughout FIGS. 1 to 8:

The feature of this modified example is that no angular displacementexists among the cam plates 13, 14a and 14b at the initial stage, andtherefore, and between the start sides 17 and 22 but that an angulardisplacement exists between the the cam grooves 20 and 24 so that thenot overlapping grooves can not allow the cam follower pin 29 to pass.In this situation the cam plates 13, 14a and 14b will not rotate even ifany inserter other than the actuator 2 is inserted into the switchassembly 1. At this stage, when the actuator 2 is inserted througheither the slit 6a or 6b, the projecting portions 7b of the actuator 2cause the cam plates 14a and 14b to rotate, and then, as shown in FIG.9(b), the recessed portion 7a comes into abutment with the start side 17of the cam plate 13. Thus the cam grooves 20 and 24 overlap so that thecam follower pin 29 can slide therein. At the same time, the cam plates13, 14 a and 14b are returned to their original position of the initialstage where an angular displacement between the cam plate 13 and the camplates 14a, 14b exists. Thereafter, they maintain the same positionwhere the cam follower pin 29 can be guided.

In this example, any trial to rotate one of the cam plates by using atool other than the actuator 2 will end in failure because the camfollower pin 29 persistently stays in the pin rest holes 21 and 25 ofthe other two cam plates whereby the cam plates remain stationary. Inthis example, as referred to above, no angular displacement exists amongthe cam plates 13, 14a and 14b at the initial stage, and a desiredangular displacement must be first produced, and thereafter thisdisplacement must be maintained so as to enable the cam plates 13, 14aand 14b to rotate to operate the operating rod 27 and the switching rod39. Thus the switch assembly is protected against a mischievous ormalicious trial to insert a tool into the switch assembly.

The example illustrated in FIGS. 2 to 4 can be assembled by assemblingthe contact-point block 3, and coupling it to the operating rod 27 ofthe block 4. The contact-point block 3 can be easily disassembled wherenecessary. The switch assemblies of the present invention are suitablefor mass-production. One of the features is in the operating rod 27which is connected to the switching rod 39 by engagement of the hooks27b and 46.

Once the protective door is closed and the normally closed contactpoints are opened and the normally opened ones are closed in accordancewith the backward movement of the switching rod 39, the switching rod islocked in this state unless it is unlocked. An unlocking device can beadded to the switch assembly. By referring to FIGS. 10 to 12, an exampleof the unlocking mechanism will be described:

A lock ledge 57 includes a base portion and an eaves portion. The baseportion has end portions 58 rotatably supported by the supports 11, andthe eaves portion extends over the cam plates 14a and 14b and terminatesat an edge portion 59 (FIG. 11). As shown in FIG. 10, the eaves portionhas a rectangular opening wide enough to cover the total width of thethree cam plates 13, 14a and 14b. As shown in FIG. 12, tile end portion58 is connected to an arm 60 extending downward and a projection 71 forsupporting a spring 75. The arm 60 is provided with a shelf 72 forsupporting a spring 76. The springs 75 are supported between theprojections 71 and recesses 73 produced on the supports 11. Likewise,the spring 76 is supported between the shelves 72 and recesses 74produced on the supports 11. The lock ledge 57 is rotatable in theclockwise direction in FIG. 11. The edge portion 59 of the lock ledge 57oppresses the peripheral surfaces of the cam plates 13, 14a and 14b.

Referring to FIG. 10, when an electro-magnet (commonly called"solenoid") is energized, the actuator releasing block 10 disengages theedge portion 59 of the locking ledge 57 from a locking recess 15a of thecam plate 13 and locking recesses 15b of the cam plates 14a and 14b. Theelectro-magnet 104 has a movable iron core 105 connected to a connectingrod 106, and a releasing ledge 107 for transmitting the motion of theconnecting rod 106 to the operating block 4. When the movable iron core105 is magnetically attracted, the releasing ledge 107 is shifted in thedirection of arrow in FIGS. 10 and 12(c), thereby rotating the arms 60in the counterclockwise direction in FIG. 12.

Referring to FIGS. 12(a) to 12(c), the operation will be described:

FIG. 12(a) shows that the recessed portion 7a and projecting portions 7bof the actuator 2 are placed into engagement with the start sides 17 and22 of the cam plates 13, and 14a and 14b. At this stage, the lock ledge57 keep contact with the surfaces of the cam plates 13, 14a and 14bstaying ahead of the locking recesses 15a and 15b.

A further advancement of the actuator 2 causes the cam plates 13, 14a,and 14b together, thereby enabling the cam follower pin 29 to shift inthe direction C in FIG. 12(a). The pin 29 reaches the point shown inFIG. 12(b) where the contact points 35 and 41 are opened and the contactpoints 37 and 43 are closed in accordance with the backward movement ofthe switching rod 39. At this moment, the edge portion 59 of the lockledge 57 fits in the locking recesses 15a and 15b and the lock ledge 57rotates in the clockwise direction. At the same time a lower part ofeach cam plate 13, 14a and 14b rests in the aperture 8 of the actuator 2so that the return sides 18 and 23 of the cam plates stand face to facewith the inside wall portion 9 of the aperture 8.

When the actuator 2 is withdrawn from the switch assembly 1, the insidewall portion 9 of the aperture 8 pushes the return sides 18 and 23,thereby forcing the cam plates 13, 14a and 14b to rotate in theclockwise direction. At this stage, if an operator tries to open thedoor intentionally or carelessly or any force acts thereon to open thedoor, the actuator 2 will be restrained from withdrawal because of theimpossibility of the cam plates 13, 14a and 14b to rotate.

The locked cam plates are released by energizing the electromagnet(solenoid) of the releasing block 10. The energization drives thereleasing ledge 107 in the direction of arrow to push the arms 60. Thestrength of the upper spring 75 is stronger than that of the lowerspring 76 so that the lock ledge 57 is rotated around the pivoted pointagainst the lower spring 76. The edge portion 59 of the lock ledge 57 isreleased from the recesses 15a, 15b. In this way the cam plates 13, 14aand 14b are unlocked.

Referring to FIGS. 13 and 14, a modified version of the switch section33 will be described:

This example is characterized in that the normally closed contact points35 and 41 are opened and the normally closed contact points 37 and 43are opened at a time interval (time lag) after the cam plates 13, 14aand 14b are locked.

A contact-point holder 61 supports the terminal plates 42 and 44 with aspace maintained by the spring 45. A return spring 49 is disposed so asto return the holder 61. The switching rod 39 moves right and left inFIG. 13 by being engaged with the operating rod 27 in theabove-mentioned manner. The switching rod 39 has a hollow body having anopen end in which a spring 70 is accommodated and a slider portion 38 onboth sides extended toward the contact-point holder 61, this sliderportion being hereinafter referred to as "slider 68". The holder 61 hasa rectangular recess 61b on each side, and a ceiling 61a having anengager 94 on the top surface. The ceiling 61a has slide rails 62 and apair of horn portions 64 extended sideways for engagement with theslider 68 in a manner described below. The rectangular recess 61b hasslide rails 63, both slide rails being for a slider 68 having a pair ofhorn portions 69 which slide on the slide rails 62 and 63. The holder 61is provided with a step 65 produced crosswise for engagement with thelower horn portions 69 of the slider 68. Normally as shown in FIGS. 13and 14, the slider 68 is biased to the left under the action of thespring 70 with the horn portions 69 being engaged with the extendedportions 64 of the ceiling 61a and the step 65 of the holder 61.

The contact-point holder 61 is provided with a box 100 in which avertically movable member 101 is accommodated. The member 101 has aslant surface which matches that of the engager 94 of the ceiling 61a.Normally as shown in FIG. 13, the member 101 is biased downward untilthe member 101 is located immediately behind the engager 94 under theaction of a spring 102. The strength of the spring 70 is larger thanthat of the spring 45.

Referring to FIGS. 15 and 16, an example of the operation of the switchassembly 1 will be described wherein FIGS. 15 show the operationoccurring when the door is closed, and FIGS. 16 show that occurring whenthe door is opened:

In FIGS. 15, before the actuator 2 is inserted into the switch assembly1, the switching rod 39 stands at its forward position (FIG. 15(a) wherethe spring 45 maintains the closure of the contact points 35 and 41(FIG. 15(a)', keeping the "on" condition.

The door is closed and the actuator 2 is inserted into the switchassembly 1. The operating rod 27 and the switching rod 39 is pushedbackward together against the spring 70 (FIG. 15(b) where the holder 61remains stationary because of a difference in strength between thesprings 70 and 102 and the slant surface of the engager 94, therebymaintaining the closure of the contact points 35 and 41 (FIG. 15(b)'.

As the switching rod 39 further advances, its backward end comes intoabutment with the holder 61 and the engager 94 pushes up the member 101(FIG. 15(c) where the cam plates 13, 14a and 14b are locked in theabove-mentioned manner, thereby preventing the switching rod 39 fromreturning (the forward movement).

Then, the member 101 comes to mount on the engager 94, thereby removingthe braking effect given by the member 101 upon the holder 61. Having nobrake, the spring 70 is set free from frustration and expands to pushthe holder 61 backward (FIG. 15(d). The contact points 43 are broughtinto contact with the fixed contact points 37 (FIG. 15(d)') under theaction of the spring 45, thereby switching on the safety switch circuit.The "on" condition of the safety switch circuit is kept under the actionof the spring 45 until the cam plates 13, 14a and 14b are unlocked bythe releasing block 10.

Now, referring to FIG. 16, the operation will be described step by stepwhen the door is opened:

An electro-magnet (solenoid) is energized to unlock the cam plates 13,14a and 14b. The opening of the door is accompanied by the withdrawal ofthe actuator 2 out of the switch assembly 1. The switching rod 39 iswithdrawn to the left (forward movement) in FIG. 16(a). The holder 61still remains stationary by the engagement of the member 101 with theengager 94.

When the switching rod 39 advances forward (to the left) to a pointwhere the horn portions 69 come into abutment with the horn portion 64and the step 65, the holder 61 follows the forward movement of theswitching rod 39 (FIG. 16(c). Since a force restraining the member 101is diminished, the spring 45 restores its strength so that the contactpoints 43 are disengaged from the points 37, thereby switching off asource of power for the machinery. When the holder 61 is furtheradvanced forward (FIG. 16(d) to where the member 101 reaches a pointnear the slant surface of the engager 94, the closure of the contactpoints 35 and 41 is restored (FIG. 16(d)'). Herein the machinery isdeenergized, and the actuator 2 is completely withdrawn out of theswitch assembly 1 (FIG. 1).

Referring to FIGS. 17, 18 and 19, a modified version of the switchsection 33 will be described:

A plastics molded terminal box 77 houses terminals 78a and 78b mountedhighest, terminals 79a and 79b next highest, terminals 80a and 80blowest, wherein the terminals 79a and 79b are normally closed, and theterminals 80a and 80b are normally opened. These six terminals arearranged three by three on either side of the operating rod. Either ofthe terminals 79a or 79b, which are normally closed, is electricallyconnected to the terminal 35 through a conductor 109, and either of theterminals 80a or 80b is electrically connected to the terminal 37through a conductor 110. The rearward end portion 108 is formed as highas the terminals 79a and 79b, and is provided with a lamp (LED) 81 inwhich multiple light emitting diodes are arranged in series connected inseries to a resistor 82, and to the terminals 78a and 78b through a leadline 84. There is provided a lens 83 on a cover 85 above the lamp 81.

Industrial Applicability

According to the present invention, the safety switch assembly can be ascompact as 9 cm(W)×2 cm(L)×3,5 cm(H). Because of the compact size, thesafety switch assembly finds many applications. The switch assembly isprotected against mischievous or malicious operation by using any othertool than the regular actuator.

We claim:
 1. A safety switch unit comprising:a switch assembly for beingattached to a structure proximate a door; an actuator for being attachedto the door proximate the switch assembly and for being inserted andlocked within the switch assembly when the door is closed, the actuatorincluding first and second portions projecting in an actuatingdirection, the second portion projecting farther than the first portion,the first and second portions being inserted into the switch assemblyalong an insertion path; a cam shaft within the switch assembly, the camshaft having an axis extending transversely with respect to theactuating direction, the axis being offset from the insertion path; afirst disc-shaped cam plate rotatably mounted on the cam shaft, thefirst cam plate having a first cam groove, a first periphery, a firstrecess in the first periphery, and a first side in the first recess, thefirst side for being initially contacted by the first portion of theactuator when the actuator is inserted within the switch assembly, thefirst cam plate being rotated by the insertion of the actuator; a seconddisc-shaped cam plate rotatably mounted on the cam shaft adjacent thefirst cam plate, the second cam plate having a second cam groove, asecond periphery, a second recess in the second periphery, and a secondside in the second recess, the second side for being initially contactedby the second portion of the actuator when the actuator is insertedwithin the switch assembly, the second cam plate being rotated by theinsertion of the actuator; a first cam follower pin moving in and alongthe first cam groove; a second cam follower pin moving in and along thesecond cam groove; an operating rod connected to the first and secondcam follower pins, the rotation of the first and second cam platesmoving the first and second cam follower pins along the respective firstand second cam grooves to axially shift the operating rod; and a switchsection for effecting safety switching operation in accordance with theaxial movement of the operating rod, the switch section having first andsecond electrical contact points forming a switch, the switch being inone of an open state and a closed state during a first phase of theinsertion of the actuator within the switch assembly before the actuatoris locked within the switch assembly, and being in the other of the openstate and the closed state during a second phase of the insertion of theactuator within the switch assembly when the actuator is locked withinthe switch assembly.
 2. The safety switch unit according to claim 1wherein the first side of the first cam plate is angularly positionedrelative to the second side of the second cam plate such that the firstportion of the actuator initially contacts the first side and the secondportion of the actuator initially contacts the second side substantiallysimultaneously, wherein the first and second cam plates rotatesubstantially simultaneously when the actuator comes into abutmenttherewith.
 3. The safety switch unit according to claim 1 wherein theswitch section comprises a light emitting diode and a lens disposed overthe light emitting diode.
 4. A safety switch unit comprising:a switchassembly for being attached to a structure proximate a door; an actuatorfor being attached to the door proximate the switch assembly and forbeing inserted and locked within the switch assembly when the door isclosed, the actuator including first and second portions projecting inan actuating direction, the second portion projecting farther than thefirst portion, the first and second portions being inserted into theswitch assembly along an insertion path; a cam shaft within the switchassembly, the cam shaft having an axis extending transversely withrespect to the actuating direction, the axis being offset from theinsertion path; a first disc-shaped cam plate rotatably mounted on thecam shaft, the first cam plate having a first cam groove, a firstperiphery, a first recess and a first locking step in the firstperiphery, and a first side in the first recess, the first side forbeing initially contacted by the first portion of the actuator when theactuator is inserted within the switch assembly, the first cam platebeing rotated by the insertion of the actuator; a second disc-shaped camplate rotatably mounted on the cam shaft adjacent the first cam plate,the second cam plate having a second cam groove, a second periphery, asecond recess and a second locking step in the second periphery, and asecond side in the second recess, the second side for being initiallycontacted by the second portion of the actuator when the actuator isinserted within the switch assembly, the second cam plate being rotatedby the insertion of the actuator; a first cam follower pin moving in andalong the first cam groove; a second cam follower pin moving in andalong the second cam groove; an operating rod connected to the first andsecond cam follower pins, the rotation of the first and second camplates moving the first and second cam follower pins along therespective first and second cam grooves to axially shift the operatingrod; a switch section for effecting safety switching operation inaccordance with the axial movement of the operating rod, the switchsection having first and second electrical contact points forming aswitch, the switch being in one of an open state and a closed stateduring a first phase of the insertion of the actuator within the switchassembly before the actuator is locked within the switch assembly, andbeing in the other of the open state and the closed state during asecond phase of the insertion of the actuator within the switch assemblywhen the actuator is locked within the switch assembly; a lock ledgerotatable on an axis parallel to the cam shaft axis and including a baseportion and an eaves portion extending over the cam plates, the eavesportion including an opening spanning across the first and second camplates, the insertion of the actuator rotating the first and second camplates to bring the first and second locking steps into releasableholding engagement with the eaves portion; and a releasing ledge forbeing selectively operated to rotate the lock ledge to move the eavesportion away from the first and second locking steps.
 5. The safetyswitch unit according to claim 4 wherein the switch section comprises astationary member having the first electrical contact point, a holderhaving the second electrical contact point, a spring elasticallyconnecting the holder to the operating rod, a restraining means forrestraining the movement of the holder during the first phase, and areleasing means for releasing the restraining means upon commencement ofthe second phase.
 6. The safety switch unit according to claim 4 whereinthe switch section comprises a light emitting diode and a lens disposedover the light emitting diode.